1. Field of the Invention
The invention relates to an initial charging method and a production method for a lithium-ion battery.
2. Description of Related Art
In recent years, a lithium-ion battery is in wide use as a secondary battery. In the lithium-ion battery, a film is formed on an electrode surface through an initial charging process. According to Japanese Patent Application Publication No. 2012-227035 (JP 2012-227035 A), for example, a solid electrolyte interface (SEI) film is formed when a carbon-based material on a surface of a negative electrode mixture layer reacts with an electrolyte in a non-aqueous electrolyte-type lithium-ion battery.
In JP 2012-227035 A, charging and discharging are repeated in a film-forming voltage region in the initial charging process for the lithium-ion battery (battery) for the formation of the SEI film. More specifically, the battery is subjected to initial charging first in a pre-charging process to be allowed to enter the film-forming voltage region. Then, a charging and discharging repetition process is started so that charging and discharging is repeated in the film-forming voltage region. Once the charging and discharging repetition process is over, the battery is charged up to a full charge voltage. The SEI film is formed when the charging and discharging is repeated as described above in the film-forming voltage region suitable for film formation.
The film-forming voltage depends on material conditions regarding a negative electrode active material, an electrolyte, an additive, and the like as well as a positive electrode active material and charging conditions. Accordingly, in some cases, the film is insufficiently formed and a sufficient output performance is not achieved even when a decomposition voltage attributable to the positive electrode active material is used as a specified voltage.